This research aims to define the course and consequences of perinatal HIV exposure and infection on neurological and psychological development during the first two years of life. It will define and describe the earliest signs and symptoms of HIV encephalopathy and will characterize the course or natural history of this disorder. These results will facilitate early recognition of HIV encephalopathy, differentiation from other causes of encephalopathy and identification of infants who may benefit from potential antiviral therapies when they become available. By incorporating a control group of matched infants, this research will test the hypotheses that: (1) Study and control infants will not differ prior to the onset of encephalopathy; (2) Some HIV- positive infants will develop a static encephalopathy with findings that are quantitatively worse than in control infants; and (3) Some HIV-positive infants will develop a dementia with findings that are qualitatively and/or quantitatively worse than in other HIV- positive infants or in control infants. Mothers at risk for HIV infection because of intravenous drug abuse, prostitution, sexual partnership with HIV-positive persons or repeated blood transfusions will be offered HIV screening during pregnancy. When their infants are born at Boston City Hospital (BCH), they will also be tested for HIV. All HIV-positive infants will form the study group (16/year). For each HIV-positive infant, two HIV-negative infants will be selected who are matched for maternal risk and perinatal experience and enrolled in the control group (32/year). All infants in both groups will be followed prospectively in the Pediatric Clinic at BCH. The protocol includes physical and neurological examination, growth assessment and development evaluation at birth, 2, 4, 6, 8, 12, 16, 20 and 24 months. Electrodiagnostic testing (EEG and visual, auditory and somatosensory evoked potentials) and psychological testing (Bayley, Farran, Stein) will be obtained at 6, 12 and 24 months. Any infant with signs or symptoms of encephalopathy will undergo additional testing (CT scan, MRI scan and lumbar puncture) and continue in the protocol. Subject enrollment will continue for three years, so that there will be approximately 50 HIV-positive study infants and 100 HIV-negative matched control infants. Epidemiological, relative risk, and statistical (MANOVA with repeated measures) determinations will be used to analyze these results and test the stated hypotheses.